test/parallel/test-fs-read-stream-concurrent-reads.js

'use strict';
const common = require('../common');
const fixtures = require('../common/fixtures');
const assert = require('assert');
const fs = require('fs');

// Test that concurrent file read streams don’t interfere with each other’s
// contents, and that the chunks generated by the reads only retain a
// 'reasonable' amount of memory.

// Refs: https://github.com/nodejs/node/issues/21967

const filename = fixtures.path('loop.js');  // Some small non-homogeneous file.
const content = fs.readFileSync(filename);

const N = 2000;
let started = 0;
let done = 0;

const arrayBuffers = new Set();

function startRead() {
  ++started;
  const chunks = [];
  fs.createReadStream(filename)
    .on('data', (chunk) => {
      chunks.push(chunk);
      arrayBuffers.add(chunk.buffer);
    })
    .on('end', common.mustCall(() => {
      if (started < N)
        startRead();
      assert.deepStrictEqual(Buffer.concat(chunks), content);
      if (++done === N) {
        const retainedMemory =
          [...arrayBuffers].map((ab) => ab.byteLength).reduce((a, b) => a + b);
        assert(retainedMemory / (N * content.length) <= 3,
               `Retaining ${retainedMemory} bytes in ABs for ${N} ` +
               `chunks of size ${content.length}`);
      }
    }));
}

// Don’t start the reads all at once – that way we would have to allocate
// a large amount of memory upfront.
for (let i = 0; i < 6; ++i)
  startRead();